(1) Field of the Invention
The present invention refers to a device and a process for profile measurement.
This can be used notably for complex contour parts such as turbine rotors, to measure the profiles of blade grooves or thin tightness tongues which are sharp peaks designed to etch the annular packing in material which can be sensitive to abrasion, to establish leaktightness by labyrinth seal. The profiles measured could be axial or circular on rotation parts.
(2) Description of Related Art
The metrological devices for profile measurement or more generally for surface contours comprise the following:    the feeler rod comparators and penetration measurement dial, which allow only rudimentary measurements,    more accurate feelers but bulky and consequently costly, situated at the end of multiple articulation passive arms fitted with travelling encoders, an example of which is described in the document FR 2 702 043,    powered feelers mounted flexibly on a moving support where the movements are measured as and when the motor moves the feeler support and when a bending of the feeler is measured: an example is described in the document U.S. Pat. No. 4,622,751; but only simple movements are possible,            non-mechanical devices using photogrammetry and based notably on the reflection of light by the surface to be measured; these are efficient but costly.        
The situation is more complicated for the pronounced contour profiles, especially widening out under the surface of the part, which is the case of the blade grooves which are connected at the surface of the part only by a narrower neck. It thus creates a problem for reaching the profile points situated at the bottom of the cavity and above all those of the overhanging parts situated under the neck. Even the feeler mounted on an articulated arm is often insufficient in spite of its flexibility as the feeler must in practice have relatively wide sections in order to possess the required mechanical resistance, and to lodge the passive measuring and maintenance motors of the articulations in stable position. For checks of such profiles, the requester already used gauge sets which were moved up and down the grooves in search of a blocking point or excessive play if any. It is obvious that the gauge sets allow only basic measurements and have the disadvantage of being specific to a given section of grooving. Another method that the requester used consisted in moulding an impression of the groove section, then extracting the mould and measuring its profile under better conditions than the profile of the groove itself. This method, very long, produced good results but was not convenient.
A simple device is being sought after to measure complex or inaccessible profiles, with considerable or hollow contours. A device both simple and inexpensive is required, easy to use and sufficiently accurate—ten or so microns or a few microns for the applications mentioned above.
It has appeared that a hand-operated feeler was the only contour follower likely to offer these advantages although those already mentioned (the comparator and the articulated arm) are clearly insufficient for different reasons.